Partial discharge (PD) detection plays a major role in the life time assessment of liquid insulation in power transformers. Many research works are being carried out to replace conventional mineral oil insulation in transformers by vegetable oils. It is necessary to understand the PD characteristics of vegetable oils before recommending them as an alternate for mineral oil. In this paper, the breakdown strength and PD characteristics of palm and corn oil were investigated in both unaged and thermally aged conditions. Laboratory experiments were performed as per IEC test procedures. PD signals were measured using wide band detection system. Phase resolved PD pattern of vegetable oils and mineral oil were compared. Effect of increase in voltage stress on the PD pattern of palm and corn oil were studied. Time and frequency domain analysis of PD pulses at needle-plane electrode configuration was carried out. Statistical analysis of PD pattern i.e. skewness and shape parameter variations with respect to applied thermal stress were also carried out. From the results, it is observed that palm and corn oils have better breakdown strength and PD characteristics even under long-term thermal stress and hence they can be used for power transformer applications.

Suwarno M. Ilyas, "Study on the Characteristics of Jatropha and Ricinnus Seed Oils as Liquid Insulating Materials", in Proceedings of the Annual Report Conference on IEEE Electrical Insulation and Dielectric Phenomena, pp.162-166, 2006.

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V.Arun and S.Chandrasekar, "Study on electrical and thermal characteristics of biodegradable vegetable oils for power transformer applications", in Proceedings of the International conference on electrical energy systems and power electronics in emerging economies, ICEESPEEE'09, SRM University, Chennai, pp.1012-1016, 16-17 Apr 2009.